EP 2 085 349 A1 discloses an example workpiece magnetic grab that includes a housing having a housing bottom that has an end face facing a workpiece to be grabbed. A magnetic piston that can be moved up and down is arranged in the housing. Disposed on the housing is a connection for a drive fluid for moving the magnetic piston so that the magnetic piston can be subjected to a first working pressure and transferred into an operating setting (i.e., an operating position). In the operating setting, the magnetic piston is positioned on or close to the housing bottom. Using a second working pressure, the magnetic piston can be transferred back into a rest setting (i.e., a rest position) into a movement chamber, in which the magnetic piston is positioned away from the housing bottom.
It can be advantageous for such magnetic grabs to automatically detect whether or not a workpiece has been picked up and whether the workpiece has been lost (e.g., dropped) during transport. Monitoring takes place via a detection device that is inserted separately into the magnetic piston and has a controllable valve having a separate permanent magnet which is guided so that it can be moved up and down in the magnetic piston, while the holding magnet is anchored in the magnetic piston.